Problem: In 42 years, Nadia will be 3 times as old as she is right now. How old is she right now?
Explanation: We can use the given information to write down an equation about Nadia's age. Let Nadia's age be $n$ In 42 years, she will be $n + 42$ years old. At that time, she will also be $3 n$ years old. Writing this information as an equation, we get: $n + 42 = 3 n$ Solving for $n$ , we get: $2 n = 42$ $n = 21$.